Various disc cartridges have been proposed as protective cases for disk-shaped signal storage media.
For example, Japanese Laid-Open Publication No. 9-153264 discloses a disc cartridge in which a disk-shaped storage medium having a single or double signal recording sides (which will be herein referred to as a “disc” simply) is completely enclosed in a disc storage portion. The disc storage portion is defined inside a cartridge body that is made up of upper and lower halves. The cartridge body includes chucking openings and a head opening. The chucking openings allow the turntable of a spindle motor and a clamper to chuck a disc inserted, while the head opening allows a head to read and/or write a signal from/on the disc. The lower one of the chucking openings is continuous with the head opening. Accordingly, while the operator carries such a cartridge, dust easily enters the inside of the cartridge through these openings and the disc is also easily soiled with finger marks. For that reason, the disc cartridge further includes a shutter for closing these openings up.
A disc cartridge having such a structure, however, has the following drawbacks. Firstly, such a disc cartridge cannot be so thin. This is because the disc storage space, defined between the upper and lower halves, should be thick enough to allow a disc drive to accurately read or write a signal (or information) from/onto the disc stored in such a disc cartridge. The reasons why the disc storage space should be relatively thick include the expected flutter or warp of the disc being rotated and an error that may occur in disposing the disc cartridge at a predetermined position inside the disc drive.
Secondly, the shutter for closing up these chucking and head openings at the same time cannot be formed at a low cost, thus increasing the overall manufacturing cost of such a disc cartridge. The reason is as follows. Specifically, the lower half of the disc cartridge is provided with an opening for the turntable of the spindle motor and a head opening, while the upper half thereof is provided with another opening for the clamper. Thus, to close these three openings up at a time, the shutter needs to be formed in a U-shape, which is not so cheap to make.
Thirdly, the disc stored inside such a disc cartridge is not fixed in many cases, thus possibly causing dust or fine particle deposition and scratching problems. Specifically, although a disc with a metal hub can be attracted and fixed in position via a magnetic force so as not to move inconstantly, an optical disc with no hub, e.g., a CD or a DVD, is normally not fixed, and movable freely, inside the disc cartridge. Accordingly, when the shutter of the disc cartridge is opened inside the disc drive, dust may enter the cartridge through its openings and be deposited on the disc easily. Also, if the disc is shaken so much as to contact with the inner walls of the disc cartridge, the signal recording side of the disc may get scratched or fine particles may be stirred up and deposited on the disc.